Many applications, such as machine manufacturing or semiconductor production, require that machine elements be held against the force of gravity while the exactly controlled vertical movement thereof nevertheless be allowed. A readily predictable performance of the gravity compensation and of the guidance is an important condition that must be met in order to achieve an accurate and rapid control of the machine element to the desired position.
The type of guide that can be used depends on the size of the required vertical positioning range. If this range is relatively small, then guides based on elastic deformation can be used. Such guides are generally referred to as spring guides. Specific examples are leaf springs or parallel spring guides.
Certain pneumatic systems for compensating for gravity are conventional, for example. However, such pneumatic systems exhibit inherent internal friction and hysteresis effects, which, moreover, can vary as a function of position and time. This makes it substantially more difficult to accurately control the position of the machine element.
Certain gravity-compensating systems based on preloaded springs are also conventional. In this case, however, the compensating spring force is dependent on the location, which, in turn, makes it difficult to accurately control the position.
A very advantageous approach for a gravity-compensated guide is the combination of a guide using leaf springs and a gravity compensation based on a passive magnetic mount.
Thus, PCT International Patent Application WO 2009/093907 describes a magnetic actuator where leaf springs having low stiffness in the axial direction and high stiffness in the radial direction form a straight guidance in the axial direction. A passive gravity compensation is achieved by an arrangement of magnets. The low positive stiffness of the leaf springs in the axial direction is compensated in the working point of the guide by a negative stiffness of the magnetic mount, so that the positional control only requires a slight compensation for gravity or for guide-induced influences.